Pressure pour or dosing furnaces can be used to discharge repeated and measured doses of a molten metal from the furnace for filing a continuous line of molds. The opening to the sprue of a mold is brought in contact with the outlet of the furnace and a gas is used to exert pressure on the molten metal in the furnace, which forces a measured dose of the melt into the sprue, through the gating system and into the mold cavities. Molds can be sequentially filed in the process.
U.S. Pat. No. 4,220,319 to Rohmann discloses a single chamber pressure pour furnace. A metered discharge from the furnace is accomplished by differential pressure sensing of air in the pressurized chamber. The pressure at which molten metal in the chamber rises to the end of the outlet tube prior to each discharge is sensed. This pressure reading is used as the baseline pressure at the start of a pour. The pour is terminated by release of pressure in the chamber when the chamber pressure reaches a selected value.
U.S. Pat. No. 5,477,907 to Meyer et al. discloses a pressure chamber that is isolated from a heating chamber by a wall with an opening through it. A backloading air regulator is used to account for the pressure increase in the pressure chamber that is required for the molten metal to rise to the end of the outlet tube before the timed period of discharge is started. Further backflow of molten metal into the heating chamber is allowed through the opening in the wall when the pressure chamber is pressurized.
U.S. Pat. No. 5,913,358 to Chadwick discloses the use of a non-return valve in the wall between the pressure chamber and heating chamber to prevent the backflow of molten metal when the pressure chamber is pressurized. The non-return valve is disclosed typically as a ball and socket valve that acts automatically to prevent reverse flow. A potential disadvantage of this arrangement is that the molten metal, or particulate in the melt, could lodge the ball in a position that permanently blocks flow of the molten metal from the heating chamber to the pressure chamber as required to replenish the supply of melt in the chamber.
U.S. Pat. No. 5,590,681 to Schaefer et al. discloses a plug valve assembly integral with upstream and down stream launder sections. The upstream launder section is connected to a low pressure casting furnace, and the upstream launder section is connected to a supply of molten metal. Flow between the supply and the low pressure casting furnace is controlled by the plug valve assembly.
One object of the present invention is to provide a pressure pour furnace wherein the pressure differential between the molten metal at a selected level in the pressure chamber and the pressurized gas used to perform a pressure pour in the pressure chamber is used to provide a repeatedly precise measured discharge of melt from the furnace. Another object of the present invention is to control the flow of molten metal to the pressure chamber of a pressure pour furnace with a compact metering valve arrangement that will also provide an efficient method of blocking backflow of the molten metal from the pressure chamber into the heating chamber, or metal supply chamber, when the pressure chamber is pressurized.